Why do I get double vision in one eye?

Q: I am a 39 years old male and am using spectacles for the past 25 yrs. For the last over 20 years the myopia level has been stable and the the lens power is - 4.5 in both the eyes. For the past three months, I am having problem in my left eye wherein I see double image. When I view an object only through my left eye, the second image appears a few millimeters to the left and a few millimeters above the original image. When I move closer to the object, the shadow image too moves closer to the original image & overlaps precisely at normal reading distance. The right eye is perfectly normal & does not show any such phenomena. The shadow image though in the same colour is less intense & less sharp. Because of this problem I have difficulty in reading printed matter at a distance owing to overlapping of letters. Also there is difficulty in recognising a person at a distance as well as driving during night. Though gradual, the extent of the problem is getting acute day by day. I have got my eyes checked at two different reputed Eye Care Centres. After carrying out various tests on the retina & cornea, I am told there is apparently no detectable problem with the eye. Both the eyes reproduce almost identical results in the tests carried out. I have been prescribed Gen Teal lubricating eye drops to be used four times a day. My blood sugar as well as blood pressure levels are normal. For the past ten months I am taking one tablet of 2.5 mg listril to regulate blood pressure. Though a bit early for my age, have started using bifocal for the last six months and the power of lens for reading is +1. I request you to kindly indicate the possible cause to the problem and suggest remedial measures.

A:You are having double vision only from your left eye. The cause of diplopia (double vision) which is uniocular (meaning from one eye only) is NOT due to neurological or eye motility problem. The problem lies somewhere in the front of the retina of the left eye (in cornea or lens). Uncorrected myopia, irregular astigmatism, lenticular astigmatism - all can be a possible reason. There are several tests that need to be done. The first is that obvious general eye examination to rule out any growth on the eyelid, corneal foreign body etc. You tell me that the eye exam was normal so these reasons can be ruled out. The second step is to do a good manifest refraction to ascertain that you are wearing the correct prescription. The third step is to wear a contact lens (rigid gas permeable preferably or soft) and to see if the problem goes away with this. My guess is that the contact lens should help you. Two valuable investigations are: 1) Corneal topography - to check for irregular corneal shape. Any LASIK laser centre should be able to do this test; 2) Wavefront analyzer - wavefront testing is a relatively new test which would be very informative in your case. You may have higher order aberrations which are causing the ghosting images out of the left eye. Most likely this is the explanation for your problem. It is really not within the scope of this reply to give you the details of what these optical aberrations are. These aberrations are usually dependent on pupil size so my guess is that your double vision varies on whether you are outside in bright sunlight (when pupil is small) or in a dark room (when pupil is large). You may talk to someone who actively follows LASIK (laser vision correction) field to get a better understanding of this concept.